Protective device



C. w. KUHN PRQTECTIVE DEVICE Filed March 8, 1926 Oct. 22, 1929 2 Sheets-Sheet INVEN To ATTORNEY Oct. 22, 1929.

c. WQKUIHN v PROTECTIVE DEVICE 2' Sheets-Sheet 2 Filed Marbh 8; 1926 I 3 IINVENTORF GXaM/rwz MW ATTORNEY Patented Oct. 22,

UNITED STATES PATENT OFFICE CLAItENCE W. KUHN, OF NORTH MILWAUKEE, WISCONSIN, AI SIGNOR, BY' MESNE ASSIGNMENTS, TO CUTLER-HAMMER, INC., A CORPORATION OF DELAWARE PROTECTIVE DEVICE Y Application filed March a, 1926. 'seriarno. 93,044.

This invention relates to protective devices for electric circuits, and whllenot limited thereto is particularly applicable to-thermoprotective devices of the selfssoldering type. Thermoprotective devices of the aforesaid character usually include a protective switch.

biased towards open position and adapted to be held in closed position through the medium of parts having an alloy metal connection therebetween. An electric heater associated with said parts effects fusion of the alloy metal connection under given electrical con ditions in the circuit to be protected to permit opening of the switch, and upon opening of the switch the heater is deenergized. The alloy metal connection then cools to re connect the aforesaid parts and the protective switch can then be reset in closed position;

The present invention has among its ob jec'ts to simplify and improve generally the construction and operation of protective devices of the aforesaid character.

Another object is to provide a protective device of the aforesaid type having improved means associated therewith for influencing the responsiveness thereof within a given range of the controlling thermic changes.

Another object is to provide an improved protective device, of the aforesaid character having its parts arranged to differently in-.

- fluence the responsiveness thereof within difdevice of the aforesaid character which is ferent ranges of the controlling thermic changes to render the same of the inverse time element type.

Another object is to provide a protective particularly adapted for protection of polyphase alternating current circuits.

Various other obj ectsand advantages of the invention will hereinafter appear.

The accompanying drawings illustrate an embodiment of the invention'which will now be described, it being understood that the embodiment illustrated is susceptible of modification without departing from. the spirit and scope of the appended claims.

In the drawing 2 is a bottom view partly in section, of the device shown in Fig.

Figs. 8 and 4 are top views partly in sec tion of certain of the parts shown in Fig. 1, illustratingthe same in different positions.

Fig. 5 is a sectional view taken substantially on line 55 of Fig. 1. v

Fig. 6 is-a side elevational view of certain of the parts shown in Figs. 1 and 3, and

Fig. 7 is a side elevational view of a modified form of heater.

Referring to Fig. 1, the same illustrates a protective switch 1 biased towards open position, a pair of thermal elements 22, each having an electric heater 3 associated therewith and a latching mechanism 4 adapted to cooperate with parts of said thermal elements to maintain said switch in closed position subject to release under given overload conditions in the circuit in which the heaters are connected.

More specifically each of the thermal elements'2 includes a .tubular member 5 having its lower end closed and of reduced diameter, as shown in Fig. 5; and a pin 6 located within said tubular member and having its lower end connected thereto by a eutectic alloy metal connection 7. The upper end of pin 6 carries an elongated star wheel 8, said star .wheel being formed of molded insulating against rotation, and under normal conditions the alloy metal connection is solid,to prevent rotation of pin 6 with respect to tube 5.

With star wheels 8 held against rotation the aforementioned latching mechanism '4 is adapted to hold switch 1 in closed position. However, under given overload conditions,

7 the heaters 3 serve to fuse one or both of the alloy metal connections 7 of the thermal elements 22 to permit rotation of one or both of the star wheels 8 for opening of switch 1.

.As before stated, the alloy metal connections 7 are eutectic, and in practice it has been found that such connections have a sharp melting and freezing point, and also expand upon freezing. Due to these characteristics of the alloy metal connections, reconnection of the pins 6 to their tubular members 5 is insured even though said pins are caused to rotate while the alloy connections are hardening.

As best shown in Fig. 3, switch 1 includes a pair of are shaped stationary contacts 11 which are fixed to an insulating panel 12 and are arranged to project outwardly between the star wheels 8 of thermal elements 2. Also, the switch 1. includes a movable bridging contact plate 13 which is fixed to a reciprocable rod 14 having an insulated opera ating knob 1 1 mounted on the outer end thereof. The inner endof rod 14 projects into an opening in panel 12 and said rod is guided at its inner end by a plate 15 and at its outer end by a bracket 16. As best shown in Fig. 6 bracket .16 is U-shaped and has an outwardly bent portion on one extremity thereof which rests on plate Plate 15 and bracket 16 and a righting plate 17, which will be hereinafter more fully described, are fixed to panel 12 by a screw 18. Rod M has a spring 19 mounted thereon which is held un- .der' compression between plate 15 and a collar 20 fixed to said rod. Rod 14 tends to move outwardly under the action offspring 19 to move the contact 13 to open position, such outward movement being limited by engagement of said contact with the outer end of bracket 16.

As best shown in Figs. 3 and 4, the latching mechanism hereinbefore mentioned includes a U-shaped member 21 arranged between the contact 13 and the collar 20 on pin 1 1. Member 21 has an enlarged opening therein for receiving pin 1 1, and the same is free to rock in a plane at right angles to the axes of the thermal elements 2. The extremities of said member are provided with latches 22, each of which is provided with a hooked portion at one end thereof extending into an opening in the U-shaped member 21. Each of said latches is biased to move outwardly with respect to the member 21 by a spring interposed between the same arid member 21, and the hook portion of each of said latches is formed to limit outward movement thereof beyond the positionshown in full lines in Fig. 3.

Assuming that the parts are-in the position shown in full lines in Fig. 3, upon depression of the rod 14 to theposition indicated by dotted lines in Fig. 3, contact 13 is moved into engagement with the stationary contacts 1.1 and is held in engagement therewith through engagement of latches 22 with the star wheels 8. As before stated, under overload conditions one or both of the star wheels 8 are released through fusion of one or both of the alloy metal connections 7. Assuming that the star wheels 8 are released simultaneously, the pawls 22 will be released simultaneously and the switch 13 willbo returned to open position under the action of spring 18 without rocking movement of the member 21. However, assuming that only one of the star wheels 8 is released as, for example, the right hand star wheel 8 in Fig. 4:, member 21 will be rocked to the position shown in full lines in this figure, and, due to this rocking movement, both of the pawls 22 will be released to permit opening of bridging contact 13.

Upon opening of the bridging contact 13 the member 21 of the latching mechanism is likely to remain in a tilted'lposition and the plate 17 hereinbefore referred to .is employed to right thc'latching mechanism upon return of the bridging contact 13 to closed position. As best shown in Fig. 4, upon full inward movement of the rod lithe extremities of the member 21 engage the plate 17 to move the same to the dotted line position shown in p Also. upon full inward movement of rod 1 1 latches 22 are held out of engage-' ment with their associated star wheels by projections 17 on plate 17. However, during initial return movement of the latches 22 from the position shown in dotted lines in Fig. t the same move out of engagement with projections 17 and simultaneously into engagementwith their associated star wheels 8, as shown indotted lines in Fig. 3.

hen the bridging contact 13 is held inthc closed position shown in dotted lines in Fig. 3 the same may be manually moved to open position by an outward pull on the knob 14 Upon out-ward pull on the knob 1% the fl'iC'. ti onal holding means for the tubes 5,'herein before mentioned, permits rotation of the thermal elements 2 by the latching mechanism, and such mechanism is thereby released to permit return of the contact 13 to open position.

The heaters 3 associated with the thermal elements 2 are arranged in opposed relation and each of the same is secured to insulating panel 12 by a pairof terminal studs 26. The heaters 3 are each provided with a helical portion 27, the axis of which is arranged in centered relation with respect to the axis of its respective thermal element. As hereinafter set forth the heaters 3 may be of various forms to render the protective device capable of use in circuits of different capacities.

The supporting means for the thermal elements 2 comprises a base 30 fixed to insulating panel 12 and a pair of cover members 31 adj ustably mounted upon said base. Each of the cover members 31 is formed of molded insulating material and the inner face of each is provided with a V-shaped groove 32 for receiving its respective thermal element and a scmicylindrical recess 33 for accommodating the helical portion 27 of the associated heat-er. The base 30 is also formed of molded insulating material and the outer face thereof is provided with grooves'34 for accommodating the thermal elements 2 and semicylindrical recesses 35 for accommodating the helical portions 27 of heaters 3. Also, the outer face of base 30 is provided with projections 36 which extend intothe recesses 33 in the cover members, and said base is suitably recessed on opposite sides thereof to receive the terminal portions of heaters 3.

Each of the thermal elements 2 is mounted upon its respective cover member 31 by means of a Ve-shaped spring wire clip 37. As best shown in Figs. 2 and 5 each of the spring clips 37 is seated within a V-shaped opening 38 in its respective cover 31 and the loop portion thereof passes aroundthe tubular memher 5 of its associated element to yieldingly hold the latter in engagement with the sides of the associated groove 32. Also, in order to prevent axial movement of the thermal elements 2 with respect to their associated cover members 31, the tubular members5 of said elements are provided with a circum ferential groove 39 for receiving the loop portion of the associated clip 37.

As before stated the cover members are adjustably mounted-upon the base and to provide for such adjustment said covers are provided with slotted openings 40 on opposite-sides thereof for receiving thimbles 41 mounted on the face of said base. Thimbles 41 are interiorly threaded, and, as shown in Fig. 2, certain of the same are secured to base 30 by screws 42 while the other thimbles are secured to base 30 byscrews 43 which also serve to secure said base to panel 12. Each of the covers 31 has its outer face recessed to receive a plate 44 and'said plates'are provided with .slotted openings for receiving screws 45 which are threaded into thi-mbles 41 and are provided with heads. for engaging said plates. The

covers 31can thus be moved to effect axial adjustment of. the thermal elements 2 with respect to heaters 3 and said covers can be readily secured in their adjusted positions by meansof the screws 45.

It is desirable to provide means for indicating the position of the thermalelements 2 with respect to heaters 3, and for'this purp'osethe plates 44 are provided with pointed projections 46 which cooperate with a scale 47. Scale 47 is fixed to a projection 48 on base 30 and the same is graduated to indicate the setting of the device.

With the foregoing arrangement of parts, the heaters 3 and the thermal elements 2 are substantially enclosed by the base 30 and covers 31. The heat supplied by the heaters 3 is supplied by radiation to the lower ends of thermal elements 2 and is also conducted by base 30 and the covers 31 to the surround ing media. It has been found that the aforedescribed arrangement is advantageous in securing the desired inverse time element of the device whereby the same is adapted to respond with varying degrees of dispatch to varying conditions of energization of the heaters 3'and also to shorten the-time element for relatively heavy overloads.

The response characteristics of the device may be varied or calibrated in numerous ways as by varying the form and dimensions of the supporting housing; by variation of "the electrothermic characteristics of the heating coils or by variation of the relative position of the heating coils and the thermal elements. In the embodiment shown the heater coils are stationary and the last men .tioned variation is effected by moving the portion 27 and an outwardly projecting por- 9 tion 28 which is in shunt with respect to said helical portion. It is apparent that by y arying the ratio of the shunt/28 with respect to the heater portion 27 the device may be employed in circuits of different current-carrying capacity.

The heaters shown in Fig. 1 are intended for use in circuits of large capacity, but for circuits of relatively small capacity heater coils of the form shown in Fig. 7 are employed. Such coils comprise a single piece of resistance wire wound to provide a helix and have terminal loops on the extremities thereof to be connected to terminal studs on panel 12.

While the aforedescribed protective device is provided with a plurality of thermal elements, .itis apparent that a single thermal element may be employed if desired. Where a single thermal element is employed the supporting member 21 of the latching mechanism is fixed to the rod 14 to prevent the aforedescribed rocking movement thereof, and said latching mechanism is thereby rendered operative to hold the switch in open position through the medium of a single thermal element.

What I claim and desire, to secure by Let ters Patent is:

1. A protective device for electric circuits comprising a circuit controlling switch, a plurality of thermally responsive elements each having an electric heater associated therewith to be included in series in the protected circuit,-and a latching mechanism adapted to cooperate with said elements to normally restrain said switch in a given position subject to release upon response of any or all of said thermal elements, said elements and their associated heaters being relatively adjustable to vary the responsiveness of the former to the latter. 7

2. A protective device for electric circuits comprising a manually operated circuit controlling switch, an electro-thermally responsive element, and a latching mechanism to cooperate with said element to normally hold said switch in a given position, subject to release under given electrical conditions in the protected circuit, said element having friction holding means associated therewith permitting manual movement of said switch out of said given position without response oi? said element.

3. In a protective device for electric circuits, in combination, a movable switch member biased towards open position, a pair of electro-thermally responsive elements arranged on opposite, sides thereof and each including a normally restrained rotary detent adapted to be released iiiulergiven elec trical conditions in the protectedcircuit, a latching device associated with said switch -niember and adapted to engage said (lGtOI'ii'S on adjacent sides thereof to hold said switch member in closed position, said latching de vice being free to rock in a plane at right lation with respect to said detents upon re- 7 closure of said switch member.

4:. A protective device for electric circuits, comprising a circuit controlling switch, a

pluralit-y of thermally responsive elements each having an electric heater associated therewith to be included in series in the protected circuit, means adapted to cooperate with said elements to normally restrain said switch in a given position subject to-release upon response of any or all of said thermal elements, said elements and their associated heaters being relatively ad ustable to vary the responsiveness of the former to the latter.

5. A thermal element for protective devices, comprising an electric heater, an 111- closing casing therefor having an adjustable part and an electro-thermally responsive device carried by said part comprising a vertically arranged tubular member having its lower end closed and arranged adjacent said heater, a pin within said tubular member, a fusible alloy metal connection in the lower end of said tubular member for connecting the latter to said pin, and a star wheel fixed to the upper end of said pin.

7. A thermal element for protective devices comprising an enclosing casing, a heater element formed from a single piece of resistance material and having a heater section arranged within said casing and a shunt sec tion outside the same and an electro-thermally responsive device arranged within said casing and associated with said heater sec: tion to respond upon'a given t t)1l'l1)01ltlli6 condition.

8. A thermal element for protective devices comprisiiig an enclosing casing, a heater element formed from a single piece of resistance material and having a heater section arranged within said casing and a shunt section outside the same and an electrothermally responsive device arranged within said casing and associated with said heater element to respond upon a given temperature condition, said thermal element and said heater section being relatively adjllStttlJlGtO vary the responsiveness of the former to the latter,

In witness whereof, I havehereunto subscribedmy name.

CLARENCE w. Kenn metal connection in the lower end of said tiibular member for connecting the latter to said pin. t

6. A thermal element for protective devices comprising an electric heater, an en- 

